This invention relates to a web laying machine of the known type which has a motor driven wheeled laying carriage travelling back and forth over a laying table. The laying carriage has a carriage chassis as well as an upper laying carriage portion which, by means of drives, is shiftable transversely to a laying direction with respect to the chassis and is rotatable about a vertical axis. On the upper laying carriage portion there is mounted a support mechanism for a web supply reel and a drive mechanism for unwinding the supply reel. The web laying machine further has a feed roll which is rotatably supported on the carriage chassis and which has an axis oriented parallel to that of the supply reel. The feed roll is driven as a function of the travelling speed of the laying carriage. On the carriage chassis there is further mounted a laying aggregate for deflecting and cutting the web.
By "web" there is meant a flexible sheet material which may be a fabric or other woven or nonwoven material and which, as stock material, has a predetermined width and generally an undetermined length.
Laying machines of the above-outlined type lay the web in individual superposed layers resulting in a web stack. In the simplest kind of web laying method no consideration has to be given to the laying direction and it is immaterial whether the same side of the web is always oriented towards the laying table. A particular type of web laying, however, is the pairwise laying of the web.
In a method of a pairwise web laying, the web, which has a first side and an opposite second side is so deposited on the laying table that in each instance on the first side of one layer there is positioned the first side of the following layer and on the second side of a layer the second side of the consecutive layer is placed. Stated differently, the web stack is built up in such a manner that in each instance the first sides and the second sides of the individual layers are in a face-to-face contacting relationship with one another. In case of the pairwise laying of the web, care has to be taken that the web has a "preferred direction" which means that the individual layers are always laid in the same direction and therefore, for example, a zigzag laying cannot be performed.
It follows from the above that a pairwise web laying is a very complex laying process because after the laying of each layer the web has to be turned over in such a manner that upon laying of the subsequent web layer in the same laying direction the web is laid with faces reversed. The turning over of the web has to be performed as rapidly as possible to save time and therefore it is an ever increasing desideratum that in a web laying machine this operation be performed substantially fully automatically. Further, also for purposes of time saving, it is generally required of web laying machines that the web taken off the supply reel be automatically threaded into the laying mechanism. In this connection, it has to be taken into consideration that the web reels may conceivably be wound in opposite directions so that the laying machine should be so designed for an automatic threading that a reverse winding direction of the supply reel does not pose any problems for the automatic threading.
German Offenlegungsschrift (published non-examined application) No. 2,922,930 discloses a web laying machine which is adapted for a pairwise laying and which performs automatic threading. The apparatus includes a laying carriage having a carriage chassis as well as an upper laying carriage portion which is mounted on the chassis and which is adapted, by means of drive arrangements, to execute shifting motions relative to the chassis and transversely to the laying direction. On the upper laying carriage portion there are mounted the web supply reel, the feed roll as well as the laying aggregate. To perform threading of the web, the supply reel is shiftable in the laying direction and may thus be positioned above the feed roll in such a manner that the web hanging from the feed roll extends on one side thereof. Subsequently, the supply reel is shifted in the laying direction such that the web lies on top of the feed roll and forms a freely hanging loop on the opposite side thereof. Thus, in the threaded condition the web hanging from the supply reel forms a loop, then extends over the feed roll and, from the feed roll side opposite the loop passes to the web laying aggregate.
In the pairwise laying of a web in the above-described prior art machine, the entire upper laying carriage portion, together with the supply reel, the feed roll and the laying aggregate is, after laying each layer, rotated through 180.degree.. The laying aggregate has to be constructed in such a manner that it permits laying in two opposite directions because otherwise the individual layers could not be laid in the same laying direction.
It is a disadvantage of the web laying machine according to the German Offenlegungsschrift No. 2,922,930 that the laying table projects on both sides of the web stack beyond the web laying machine at least by the width thereof because, due to the rotation of the upper laying carriage portion together with the laying aggregate, the laying machine must be capable of moving transversely beyond the web stack in both directions. It is a further disadvantage of this machine that, because of the turning of the laying aggregate together with the upper laying carriage part, that side also changes continuously on which the laying aggregate lays the web and thus a visual monitoring of the web stack, for example, to detect defects, is more difficult. This is particularly the case if the laying aggregate lays the web upstream of the laying carriage--as viewed in the laying direction--and the operating person may visually monitor only that part of the web which is visible downstream of the laying carriage. Consequently, cutting out the defective web areas is also significantly more difficult.
It is a further disadvantage of the known web laying machine that in case of different unwinding directions of the supply reels, a different positioning thereof above the feed roll is necessary because dependent upon the unwinding direction, the web hangs from the supply reel on different sides of the axis thereof and therefore its distance from the feed roll will differ by the thickness of the supply reel.
The above-discussed disadvantages are eliminated from another known web laying machine in which the laying aggregate as well as the supply roll are non-shiftably mounted on the carriage chassis. The upper laying carriage portion carries only the support mechanism for the supply reel which is situated directly above a rotary point defined by the rotary axis of the upper laying carriage portion and is non-shiftably mounted thereon. In order to guide the web, taken from the supply reel, in the zone of the feed roll for the purpose of threading, the upper laying carriage portion is further provided with a conveyor belt situated underneath the supply reel and extending parallel to the laying direction. The conveyor belt advances the web, hanging from the supply reel, in the direction of the feed roll so that thereafter the web will hang from a front edge of the conveyor belt situated above the feed roll, onto one side of the feed roll and may be trained around the feed roll by means of a deflecting roller movable above the feed roll.
In the pairwise web laying by such a laying machine, for performing a web reversal after laying a web layer, the web is rewound on the supply reel, that is, the web is pulled out (unthreaded) from the laying mechanism, then the upper laying carriage portion is rotated 180.degree. and thereafter the web is again threaded into the laying mechanism so that the new layer may be deposited in the same direction as the previous layer, but with the web faces reversed. This then means that for a substantially automated reversal of the web subsequent to the laying of a web layer, the unthreading of the web from, and its rethreading into the laying mechanism and the rotation of the upper laying carriage portion by 180.degree. has to be performed automatically.
In an upper laying carriage portion of the above-outlined construction, however, difficulties are encountered during the threading as well as during the web laying as concerns a synchronization of the delivery speed of the web, the speed with which the web is unwound as well as the rpm of the feed roll.
During the unthreading and threading of the web in the above-outlined machine, the supply speed of the web has to be greater than the unwinding speed with which the web runs off the supply reel, because otherwise risks are high that the web will be positioned obliquely on the conveyor belt and thus the web would hang at an inclination in the zone of the feed roll and also, it would be threaded in an oblique orientation. Such occurrences are undesired because during the subsequent laying of the web, folds in the individual layers may appear. Further, the conveyor belt has to be continuously driven during the web laying because a frontal edge of the conveyor belt situated above the supply roll serves as a deflecting edge for the web pulled from the supply reel to the feed roll. In such a case the unwinding speed from the supply reel and the speed of the conveyor belt must be accurately synchronized with the rpm of the feed roll which, in turn, has to be coupled with the travelling speed of the laying carriage. Otherwise, risks are high that during the laying operation the web, because of an insufficient synchronization of the individual speeds, is brought to the feed roll misaligned or with folds which eventually result in a non-uniform laying or the formation of folds in the layers.